The verb trasalire should be conjugated (I report the Indicative present tense) as
Io trasalisco; Tu trasalisci, Egli trasalisce ...
But since the verb may be perceived as a composite of salire, it is often used with its conjugation:
Io trasalgo; Ti trasali; Egli trasale ...
I'm sure this is not the only case of this phenomenon. Do you know to which extent this mechanism of compositional usage of a root is accepted by the speaking community and the official grammars?